This project examines the role(s) of the gram negative oral microorganism Cytophaga sp. in the initiation, development and progression of periodontal diseases. These bacteria are constituents of dental plaque and are strongly implicated in the pathogenesis of destructive periodontitis. A series of monoclonal antibodies have been developed, utilizing both rat and mouse, with specificity for human oral isolates of Cytophaga sp. and the related species, Capnocytophaga. These reagents have been used to demonstrate the heterogeneity of these species as they exist in the oral cavity. These antibodies are useful as well in continuing studies of attachment and aggregation of these bacteria. Attachment of bacteria to the tooth surface or aggregation to previously attached bacteria represents the initial step in the periodontal disease process. An in vitro attachment assay has been developed for Cytophaga sp. bacteria to examine mechanisms of attachment and the role of serum and serum-dirived factors in the attachment process.